1. Field of the Invention
The present invention relates to a transparent photocathode and a photoelectric tube utilizing the transparent photocathode.
2. Related Background Art
As a transparent photocathode having high sensitivity to an infrared region, the transparent photocathode disclosed in "Japanese Patent Publication No. 3-57572 (57572/1991)" has been known. In this transparent photocathode, a silver layer, a silver oxide layer, a potassium layer, a silver layer, a cesium layer, and a silver layer are deposited on a glass substrate in order. Further, in this publication, a transparent photocathode in which a silver layer, a silver oxide layer, a potassium layer, a cesium layer, and a silver layer are deposited on a glass substrate is also disclosed. In the conventional techniques including the techniques disclosed in the aforementioned publication, the diameter of the silver particles forming a silver layer on a transparent substrate is within the range of 50 to 70 nm for all particles. A particle diameter in the silver layer of the conventional products is obtained with use of SEMS (scanning electron microscopes).
However, in the aforementioned transparent photocathodes, the former has the sensitivity up to about 1.4-1.6 .mu.m wavelength, whereas the latter has the sensitivity up to about 1.2 .mu.m wavelength, but both do not have the sensitivity to the long wavelength region and their quantum efficiencies are insufficient. Further, the former has the sensitivity to near 1.5 .mu.m wavelength but also has the high sensitivity to near infrared or visible light the wavelength of which is shorter. Because of this, if the former is applied to, e.g., a light communication system, disturbance noise is produced.